A polarizer element, particularly a polarizing beam splitter, is an element in which a specific polarized light is obtained at different angles of propagation which depend on the direction of polarization of two orthogonally polarized components of an incident light.
Conventional polarizing beam splitters, such as the Glan-Thompson prism or Rochon prism, include an element using a crystal with enhanced birefringence in which a light path is split due to the difference between refraction angles or total reflection angles of two orthogonally polarized components of light at the reflection plane of the crystal. In addition, the conventional polarizing beam splitter includes an element using a total reflection prism which consists of an isotropic optical medium such as glass and provided with a multilayer dielectric film formed on the reflection plane thereof whereby light is totally reflected, or otherwise transmitted, in accordance with refractive indices of polarized components.
These conventional elements, however, have a disadvantage that they are large in size, low in production efficiency and expensive.
The reflection boundary surface in these conventional elements is slanted by at least 45 degrees relative to the light axis. Therefore, such an element has to take the form of a cube having a side no less than .sqroot.2 times a diameter of the light beam to be transmitted. Specifically, the side of the cube is as long as 8 to 10 mm where the conventional polarizer element is applied to an optical disc recording or reproducing apparatus.
Another type of a conventional polarizer element is disclosed in "National conference record, 1982, Optical & Radio Wave Electronics, the Institute of Electronics & Communication Engineers of Japan, Part 2". The conventional polarizer element consists of a birefringent tapered plate of Rutile (TiO.sub.2) having a tapered angle of 4 degrees. When parallel light beam is incident to the birefringent tapered plate on one side thereof, the parallel light beam is subject to different refractions between an extraordinary ray component and an ordinary ray component, so that the two components are split on the other side of the birefringent tapered plate with a split angle of approximately 1 degree.
The birefringent tapered plate, however, is associated with a disadvantage that a fabricating process is complicated, because the cutting of a tapered configuration is difficult on a mass-production basis, and the polishing of a tapered surfaces is also difficult to be carried out. There is a further disadvantage that Rutile is expensive.